IC packages serve to space transform the I/O of an IC chip to a pattern and pitch which is more suitable to the needs of a next level interconnection device. The next level device may be another IC package, an electronic module or an interconnection substrate such as a printed circuit board (PCB). IC packages are thus created in a wide variety of different constructions based on the requirements of the application ands the number of input/output (I/O) terminals on the die. The package constructions themselves vary from chip scale and wafer level packages created near or at the size of the IC die, to leadframe type structures, to highly complex multi layer interconnection structures all of which serve to translate the I/O on the chip from a fine pitch to a more useful pitch.
IC package substrate structures, especially those used for high performance applications, are designed with great care in an effort to precisely control the characteristic impedance of the electronic signal from the chip to the next level interconnection device. Due to the complexities of the traditional approach to design, manufacture and assembly, signal quality is often degraded or compromised by the intrinsic frailties and inefficiencies of those same design and interconnection manufacturing technologies employed in the creation of higher performance IC packages. Some relief can be obtained by use of more exotic materials which provide a more acceptable signal quality, however, those gains are achievable only at costs that often exceed in multiples the cost of IC they are packaging. While solutions continue to be developed to solve the electrical problems, optical interconnections will be similarly challenged as optical IC solutions come of age. Moreover, it is anticipated that both electrical and optical solutions will be required on a common IC in the near future.
In general, transmission of high speed signals, whether achieved electrically using metal or other conductive materials or optically using optical fiber, requires that precise control of the structure and materials be maintained at every point along the transmission path, starting at the chip itself, to ensure the quality of the transmitted signal. Any disruptions along the transmission path will degrade signal quality. Thus there is present and future need for improved IC package and interconnection structures and alternative interconnection methods that will meet the needs of both high speed electrical and optical interconnections both separately and together and in doing so meet the performance and cost demands of next generation electronic products.